[RFC PATCH dm-ioband] Added in blktrace msgs for dm-ioband

[Alan D. Brunelle]

This is a multi-part message in MIME format.Hi Ryo -

I don't know if you are taking in patches, but whilst trying to uncover
some odd behavior I added some blktrace messages to dm-ioband-ctl.c. If
you're keeping one code base for old stuff (2.6.18-ish RHEL stuff) and
upstream you'll have to #if around these (the blktrace message stuff
came in around 2.6.26 or 27 I think).

My test case was to take a single 400GB storage device, put two 200GB
partitions on it and then see what the "penalty" or overhead for adding
dm-ioband on top. To do this I simply created an ext2 FS on each
partition in parallel (two processes each doing a mkfs to one of the
partitions). Then I put two dm-ioband devices on top of the two
partitions (setting the weight to 100 in both cases - thus they should
have equal access).

Using default values I was seeing /very/ large differences - on the
order of 3X. When I bumped the number of tokens to a large number
(10,240) the timings got much closer (<2%). I have found that using
weight-iosize performs worse than weight (closer to 5% penalty).

I'll try to formalize these results as I go forward and report out on
them. In any event, I thought I'd share this patch with you if you are
interested...

Here's a sampling from some blktrace output (sorry for the wrapping) - I
should note that I'm a bit scared to see such large numbers of holds
going on when the token count should be >5,000 for each device...
Holding these back in an equal access situation is inhibiting the block
I/O layer to merge (most) of these (as mkfs performs lots & lots of
small but sequential I/Os).

...
  8,80  16        0     0.090651446     0  m   N ioband 1 hold_nrm 1654
  8,80  16        0     0.090653575     0  m   N ioband 1 hold_nrm 1655
  8,80  16        0     0.090655694     0  m   N ioband 1 hold_nrm 1656
  8,80  16        0     0.090657609     0  m   N ioband 1 hold_nrm 1657
  8,80  16        0     0.090659554     0  m   N ioband 1 hold_nrm 1658
  8,80  16        0     0.090661327     0  m   N ioband 1 hold_nrm 1659
  8,80  16        0     0.090666237     0  m   N ioband 1 hold_nrm 1660
  8,80  16    53036     0.090675081  4713  C   W 391420657 + 1024 [0]
  8,80  16    53037     0.090913365  4713  D   W 392995569 + 1024
[mkfs.ext2]
  8,80  16        0     0.090950380     0  m   N ioband 1 add_iss 1659 1659
  8,80  16        0     0.090951296     0  m   N ioband 1 add_iss 1658 1658
  8,80  16        0     0.090951870     0  m   N ioband 1 add_iss 1657 1657
  8,80  16        0     0.090952416     0  m   N ioband 1 add_iss 1656 1656
  8,80  16        0     0.090952965     0  m   N ioband 1 add_iss 1655 1655
  8,80  16        0     0.090953517     0  m   N ioband 1 add_iss 1654 1654
  8,80  16        0     0.090954064     0  m   N ioband 1 add_iss 1653 1653
  8,80  16        0     0.090954610     0  m   N ioband 1 add_iss 1652 1652
  8,80  16        0     0.090955280     0  m   N ioband 1 add_iss 1651 1651
  8,80  16        0     0.090956495     0  m   N ioband 1 pop_iss
  8,80  16    53038     0.090957387  4659  A  WS 396655745 + 8 <- (8,82)
6030744
  8,80  16    53039     0.090957561  4659  Q  WS 396655745 + 8 [kioband/16]
  8,80  16    53040     0.090958328  4659  M  WS 396655745 + 8 [kioband/16]
  8,80  16        0     0.090959595     0  m   N ioband 1 pop_iss
  8,80  16    53041     0.090959754  4659  A  WS 396655753 + 8 <- (8,82)
6030752
  8,80  16    53042     0.090960007  4659  Q  WS 396655753 + 8 [kioband/16]
  8,80  16    53043     0.090960402  4659  M  WS 396655753 + 8 [kioband/16]
  8,80  16        0     0.090960962     0  m   N ioband 1 pop_iss
  8,80  16    53044     0.090961104  4659  A  WS 396655761 + 8 <- (8,82)
6030760
  8,80  16    53045     0.090961231  4659  Q  WS 396655761 + 8 [kioband/16]
  8,80  16    53046     0.090961496  4659  M  WS 396655761 + 8 [kioband/16]
  8,80  16        0     0.090961995     0  m   N ioband 1 pop_iss
  8,80  16    53047     0.090962117  4659  A  WS 396655769 + 8 <- (8,82)
6030768
  8,80  16    53048     0.090962222  4659  Q  WS 396655769 + 8 [kioband/16]
  8,80  16    53049     0.090962530  4659  M  WS 396655769 + 8 [kioband/16]
  8,80  16        0     0.090962974     0  m   N ioband 1 pop_iss
  8,80  16    53050     0.090963095  4659  A  WS 396655777 + 8 <- (8,82)
6030776
  8,80  16    53051     0.090963334  4659  Q  WS 396655777 + 8 [kioband/16]
  8,80  16    53052     0.090963518  4659  M  WS 396655777 + 8 [kioband/16]
  8,80  16        0     0.090963985     0  m   N ioband 1 pop_iss
  8,80  16    53053     0.090964220  4659  A  WS 396655785 + 8 <- (8,82)
6030784
  8,80  16    53054     0.090964327  4659  Q  WS 396655785 + 8 [kioband/16]
  8,80  16    53055     0.090964632  4659  M  WS 396655785 + 8 [kioband/16]
  8,80  16        0     0.090965094     0  m   N ioband 1 pop_iss
  8,80  16    53056     0.090965218  4659  A  WS 396655793 + 8 <- (8,82)
6030792
  8,80  16    53057     0.090965324  4659  Q  WS 396655793 + 8 [kioband/16]
  8,80  16    53058     0.090965548  4659  M  WS 396655793 + 8 [kioband/16]
  8,80  16        0     0.090965991     0  m   N ioband 1 pop_iss
  8,80  16    53059     0.090966112  4659  A  WS 396655801 + 8 <- (8,82)
6030800
  8,80  16    53060     0.090966221  4659  Q  WS 396655801 + 8 [kioband/16]
  8,80  16    53061     0.090966526  4659  M  WS 396655801 + 8 [kioband/16]
  8,80  16        0     0.090966944     0  m   N ioband 1 pop_iss
  8,80  16    53062     0.090967065  4659  A  WS 396655809 + 8 <- (8,82)
6030808
  8,80  16    53063     0.090967173  4659  Q  WS 396655809 + 8 [kioband/16]
  8,80  16    53064     0.090967383  4659  M  WS 396655809 + 8 [kioband/16]
  8,80  16        0     0.090968394     0  m   N ioband 1 add_iss 1650 1650
  8,80  16        0     0.090969068     0  m   N ioband 1 add_iss 1649 1649
  8,80  16        0     0.090969684     0  m   N ioband 1 add_iss 1648 1648
...

Regards,
Alan D. Brunelle
Hewlett-Packard